# Wireless Power

9 Steps

## Step 3: The Secondary Coil

This circuit is one of the simplest you can ever create. It is composed of magnet wire coil but smaller like the primary, a 0.02uF
capacitor also like the primary, and some leads you can attach things to. For LED's the circuit looks like that. Yet, for powering your iPod and other devices that use DC power you need a diode bridge, or rectifier which can turn AC into DC to power your portable device. Take a look for yourself that the secondary coil has an AC output which will only power LED's.

Remove these ads by Signing Up
randomtwig says: Apr 4, 2013. 12:19 PM
Hi Hi. Just wondering if the power loss across the air gap is significant enough to render this inefficient?
MadScientist101 says: May 5, 2011. 1:11 PM
can you give us some sort of ratio of primary to secondary windings or how you wound yours as it would be of great help
thanks
acmefixer says: Sep 9, 2009. 8:05 AM
As someone else stated, the two capacitors are in series, so the actual value is .0.005 uF or 5 nF. This value across the coil creastes a parallel tuned tank circuit which resonates at some frequency determined by the coil inductance (the .005 uF is fixed). This inductance is determined by the number of turns you put on the coil. I would suggest varying the frequency to see where the best results are, since the author gave no specifics about how big the coil was and how many turns it had. Also, the LED is a light emitting DIODE, and hence rectifies the AC like a diode. But it takes over 2 volts to light up a red LED, and even more for other colors. It might give better power transfer if more turns were added to the coil, and lower capacitance used. Also, 1N5817 schottky rectifier and filter capacitor could be used to rectify the coil's AC to a DC, and then a voltage boost circuit such as a Joule Thief could be used to extract even more power out of the coil. But the real problem is that the output of the function generator is very low. In the schematic of the function generator, they show that only one of the 'HC04 inverters is used, the other four are not used. I ordered one, and the first thing I'm going to do is cut the circuit board traces and add the other four inverters in parallel with the output. That will give a lot more output current. Another thought. The function generator could be replaced with a simple Joule Thief circuit. The big coil would be the main JT coil, and another coil would be added for the feedback coil. Once the JT 'transmitter' is working, the receiving coil would be tuned to the transmitter's frequency. JTs work around this frequency, in the 50 to 200 kHz range.
oakvillan in reply to acmefixerApr 24, 2011. 6:03 PM
Exactly how would you go about doing that?
I know what a Joule Thief circuit is and how you make one, but I want to know how you would wire it if you were to actually replace the function generator with the circuit.
acmefixer in reply to oakvillanApr 24, 2011. 10:49 PM

Here is one air core JT I recently made. You would have to make the air core coil larger.
Mar 10, 2011. 10:36 AM
here two capacitor of value .01 uf are connected in parallel or series???????
njschott in reply to abhishek79shrivastavaMar 14, 2011. 3:06 PM
Parallel.
Mar 10, 2011. 10:35 AM
can you tell me the number of turns in secondary coil and size of sec. coil.
also tell the exact no. of turns and size of primary coil
abhishek79shrivastava@gmail.com
robotkid249 (author) says: May 12, 2009. 8:21 PM
Sorry for the confusion the theoretical circuit diagram is only a ac to dc converter. The secondary circuit goes to the input of the ac to dc converter. I will post a different schematic showing all of the circuitry tomarow.
tanmanknex in reply to robotkid249May 13, 2009. 5:47 AM
Would using this to charge an ipod touch a/o cell phone be too risky? doesn't magnetism ruin things like that? also, what would i have to do to get it to work for me?
hemmikarl in reply to tanmanknexMay 15, 2009. 7:59 PM
cell phone should be ok but i still wouldn't do it but ipod touch or any ipod is a horrible idea (some have harddrives)
TyMan210 in reply to hemmikarlDec 17, 2009. 11:47 PM
Only the iPod mini and the iPod photo have hard drives. Unless, you have an old Classic.
hemmikarl in reply to TyMan210Dec 18, 2009. 4:31 AM
Ipod classic has also a hard drive...
also Ipod video V5 and older....
so I have had 2 ipods and both have had hard drives... so you can´t say that only the ipod mini and photo have hard drives...
if it's lagrer than 20gb it probobly has a hard drive...

TyMan210 in reply to hemmikarlDec 18, 2009. 12:24 PM
What I mean is, the Mini and Photo are the only ones that weren't upgraded to flash memory. That's why I said have not had.
tanmanknex in reply to hemmikarlMay 15, 2009. 10:29 PM
all of the newer ones are flash but i'm going to do it to cell phone only (probably) seeing as i already have a good charger for my ipod.
lioneyexp says: May 16, 2009. 7:49 PM
how much energy is lost from the large coil to the smaller one?
tanmanknex in reply to lioneyexpMay 16, 2009. 11:38 PM
depends on quite a few things. one of them is distance. see comment further down about a 1:1 ratio.
gxb5443 says: May 12, 2009. 12:30 PM
Do the inductances have to match between the two coils have to be the same?
evildoctorbluetooth in reply to gxb5443May 14, 2009. 7:31 AM
no, however the number of coils on both sides along with the distance between them (called the mutually inducive element) and the load you use will affect the applied emf to the secondary circuit.
gxb5443 in reply to evildoctorbluetoothMay 14, 2009. 10:52 PM
the load will have effect? How do you take that into account? So this way is just two arbitrary coils that will couple together. If you tuned the base and receiver to be in resonance, wouldn't that transfer as close to 100% power transfer as you can get?
gxb5443 in reply to evildoctorbluetoothMay 14, 2009. 11:15 AM
oh so this will transfer power no matter what. If the the base and reciever were tuned to one another though there would be way greater efficiency, right?
evildoctorbluetooth in reply to gxb5443May 15, 2009. 7:14 AM
If the Circuit reached resonance, there would be voltage/current magnification, which you may have to consider when choosing your components. the advantage would be that energy would only be dispersed A, in the resistive element, and in the space between the coils. i looked it up, and every time the distance doubles, you lose magnetic power by a factor of 4.
sabre says: May 12, 2009. 1:28 PM
LED's arent meant for AC current. its a light emmitting diode, meaning it only allows electricity to pass through in one direction.
tboehmer in reply to sabreMay 14, 2009. 8:08 AM
Since the frequency is so high our eyes can't perceive the difference (only in brightness maybe), so inserting diodes pointless (and redundant if you did a half-wave rectifier).
robomaniac in reply to sabreMay 12, 2009. 5:06 PM
It does not matter, the LED will glow when the sine wave is on the positive side. You will not break the LED by doing so.
ChunkMunk01 says: May 12, 2009. 7:45 PM
Hey guy, Just wondering how much electronics experience you really have. When you wire two capacitors in SERIES as your picture shows, their series capacitance does not increase, only their breakdown voltage, as the voltage is divided by the two devices in series. To add capacitances with capacitors, you wire them in parallel. PS. on the last page of the instructable, your full wave rectifier schematic shows your 4 diode bridge, your two wires for dc out, and two capacitors of different values in PARALLEL, which is redundant unless you're adding the capacitive values to find a resonant frequency. Seeing as how their purpose is to smooth the output of the rectifier, in general, the bigger the better. done and done.
lorikix says: May 12, 2009. 8:36 AM
Do you have a simple circuit diagram you can show us?